3-Hydroxyisobutyryl-CoA hydrolase (HIBCH) deficiency is an autosomal recessive disorder characterized by episodes of ketoacidosis and a Leigh-like basal ganglia disease, without high concentrations of pyruvate and lactate in the cerebrospinal fluid. Only 4 cases of HIBCH deficiency have been reported. However, clinical&ndash;biochemical correlation in HIBCH deficiency by determining the detailed residual enzyme activities has not yet been elucidated. Here, we report a case of two Japanese siblings with HIBCH deficiency carrying a new homozygous missense mutation (c.287C&nbsp;&gt;&nbsp;A, [p.A96D]) at the substrate-binding site. A transfection study using HIBCH expression vectors harboring wild type or 4 reported mutations, including the newly identified mutation (p.A96D, p.Y122C, p.G317E, and p.K74Lfs*13), revealed a correlation between residual HIBCH activities and the severity of the disease. All HIBCH mutants, except p.K74Lfs*13, showed residual enzyme activity and only the patient with p.K74Lfs*13 had congenital anomalies. p.G317E showed only low enzyme activity (~&nbsp;3%) of that of wild-type HIBCH. Although p.A96D had approximately 7 times higher enzyme activity than p.G317E, patients with p.A96D died during childhood. These findings are essential for clinical management, genetic counseling, and specific meal and concomitant drug considerations as part of the treatment for patients with HIBCH deficiency.

Mentions:
The HIBCH activity in patient II-4 lymphoblastoid cells was decreased to 35% of that of the healthy controls' cells (Fig. 3A). A transfection study showed that transient expression of pHIBCH increased the level of HIBCH activity approximately 5-fold when compared with that in control cells mock transfected with p3 × FLAG-CMV. HIBCH activity in cells transiently expressing the HIBCH mutants p.A96D, p.Y122C, p.G317E, or p.K74Lfs*13 were 22%, 55%, 3%, and 0% of the wild-type HIBCH activity, respectively (Fig. 3B). Western blot analysis demonstrated that the amounts of HIBCH harboring p.A96D and p.Y122C mutations were the same as that of wild type. However, the amount of HIBCH harboring the p.G317E mutation decreased, while HIBCH harboring the frameshift mutation (p.K74Lfs*13) was not detected (Fig. 3B). The mean Km of HIBCH in the cells of patient II-4 and in 3 control lymphoblastoid cells was determined to be 20.1 μM and 3.7 μM, respectively (Fig. 3C).

Mentions:
The HIBCH activity in patient II-4 lymphoblastoid cells was decreased to 35% of that of the healthy controls' cells (Fig. 3A). A transfection study showed that transient expression of pHIBCH increased the level of HIBCH activity approximately 5-fold when compared with that in control cells mock transfected with p3 × FLAG-CMV. HIBCH activity in cells transiently expressing the HIBCH mutants p.A96D, p.Y122C, p.G317E, or p.K74Lfs*13 were 22%, 55%, 3%, and 0% of the wild-type HIBCH activity, respectively (Fig. 3B). Western blot analysis demonstrated that the amounts of HIBCH harboring p.A96D and p.Y122C mutations were the same as that of wild type. However, the amount of HIBCH harboring the p.G317E mutation decreased, while HIBCH harboring the frameshift mutation (p.K74Lfs*13) was not detected (Fig. 3B). The mean Km of HIBCH in the cells of patient II-4 and in 3 control lymphoblastoid cells was determined to be 20.1 μM and 3.7 μM, respectively (Fig. 3C).

3-Hydroxyisobutyryl-CoA hydrolase (HIBCH) deficiency is an autosomal recessive disorder characterized by episodes of ketoacidosis and a Leigh-like basal ganglia disease, without high concentrations of pyruvate and lactate in the cerebrospinal fluid. Only 4 cases of HIBCH deficiency have been reported. However, clinical&ndash;biochemical correlation in HIBCH deficiency by determining the detailed residual enzyme activities has not yet been elucidated. Here, we report a case of two Japanese siblings with HIBCH deficiency carrying a new homozygous missense mutation (c.287C&nbsp;&gt;&nbsp;A, [p.A96D]) at the substrate-binding site. A transfection study using HIBCH expression vectors harboring wild type or 4 reported mutations, including the newly identified mutation (p.A96D, p.Y122C, p.G317E, and p.K74Lfs*13), revealed a correlation between residual HIBCH activities and the severity of the disease. All HIBCH mutants, except p.K74Lfs*13, showed residual enzyme activity and only the patient with p.K74Lfs*13 had congenital anomalies. p.G317E showed only low enzyme activity (~&nbsp;3%) of that of wild-type HIBCH. Although p.A96D had approximately 7 times higher enzyme activity than p.G317E, patients with p.A96D died during childhood. These findings are essential for clinical management, genetic counseling, and specific meal and concomitant drug considerations as part of the treatment for patients with HIBCH deficiency.